BIOLOGY WATER AND SOLUTIONS PAGE 39 44 LECTURE

BIOLOGY WATER AND SOLUTIONS PAGE 39 -44

LECTURE 1 OBJECTIVES �BY THE END OF THIS LECTURE, YOU WILL BE ABLE TO: 1. Explain how water’s polar nature affects its ability to dissolve substances. 2. Outline the relationship between hydrogen bonding and the different properties of water.

CORNELL NOTES

WATER! �Water is essential to life because of its structure �The water molecule is one oxygen atom and two hydrogen atoms that are bonded COVALENTLY (they share electrons) �See pics on page 39 of text

POLARITY �The total charge on a water molecule is NEUTRAL (no charge) BUT the charge is not the same on both sides �Water is called a POLAR molecule because the charge is different on 2 sides

SOLUBILITY OF WATER �Because a water molecule is POLAR, other polar molecules will dissolve easily in water OPPOSITES ATTRACT!

HYDROGEN BONDING �Because water is POLAR water molecules stick to themselves �Water molecules are held to each other by HYDROGEN BONDS �These bonds form, break, and reform A LOT

1 st PROPERTY OF WATER: �Water molecules sticking to each other is called COHESION �Water molecules sticking to something else (like glass) is called ADHESION

2 nd PROPERTY OF WATER: �TEMPERATURE MODERATION Water has a HIGH HEAT CAPACITY, which means it can absorb or release a lot of energy without a big change in temperature The temperature of water goes up only after all the hydrogen bonds are broken

Examples: Example: The oceans stabilize global temperatures Example: Organisms can keep their cells (that are mostly water) the same temp. even though the outside temp. changes Example: Sweating water which releases body heat

3 rd PROPERTY OF WATER: �DENSITY OF ICE: Because the hydrogen bonds form at a certain angle there is a lot of space between molecules when frozen So, ice (which is a SOLID) is LESS dense than water (which is a LIQUID) Bodies of water freeze from top down, allowing life to exist below icy surface

REVIEW: 1. 2. Explain how water’s polar nature affects its ability to dissolve substances: Outline the relationship between hydrogen bonding and the different properties of water: